Field of the Invention
This invention relates generally to the field of plasmonic nanostructure sensors and methods for detection and quantification of biological, chemical, or biochemical molecules and compounds through plasmonic Fano resonance signaling.
Description of the Related Art
The ability to detect biological, chemical, and biochemical analytes such as proteins, DNA, RNA, enzymes, viral particles, prions, toxins, and non-biologic small molecules such as drugs and drug metabolites is extremely important in life sciences research as well as in personalized medicine. Such detection in point-of-care diagnostics allows early detection of analytes associated with a particular disease state or predisposition which can then be followed through with the appropriate treatment. Likewise, the detection of chemical molecules and small molecule drugs and drug metabolites has a wide range of ramifications both within and outside the clinic.
Traditionally, such detection has been limited by the use of systems and equipment requiring labels such as fluorescent dyes and radiolabels that can change conformation of the analyte and often require time-consuming steps and substantial and specialized equipment. Further, traditional detection techniques such as immunoassays, DNA sequencing, polymerase chain reaction (PCR), and cell and tissue-culture are not conducive to point-of-care diagnostics in that the equipment for carrying out these extensive tests are not readily available in a physician's office, and the results from the tests take days if not weeks to obtain.
Recently, plasmonic biosensors using nanostructures for detection of specific biomolecules and chemicals with the naked eye have been developed, which are considered a breakthrough for point-of-care diagnostics. See U.S. Pat. No. 7,612,883, US 2008/0280374 A1, US2008/0285039 A1, US 2008/0278728 A1, WO 2011/106057, WO 2010/099805, WO 2008/136734, and WO 2008/039212. The art describes how nanostructure biosensor platforms can be constructed using substrates, metal films, periodically arranged nanoelements (particularly nanoholes), and capture agents such as ligands that can bind specific analytes.
The plasmonic sensor detection technique essentially employs a light source with a plasmonic nanostructure sensor that contains a test portion for testing a particular analyte, and utilizes certain optical transmission effects of the nanoholes that can be detected with the naked eye, or with a simple detection mechanism. These techniques generally rely on various surface photonic phenomenon observed in nanoholes due to light and/or electromagnetic waves trapped at the metal/dielectric interfaces of these nanostructure platforms.
One such biosensor device is based on asymmetric Fano resonances, a wave phenomenon, that is observed in plasmonic nanoholes. Yanik, et al., Seeing Protein Monolayers With Naked Eye Through Plasmonic Fano Resonances, Proceedings of the National Academy of Sciences of the United States of America (PNAS), vol. 108, no. 29, 11784-789 (Jul. 19, 2011). A Fano resonance is a type of resonant scattering phenomenon that gives rise to an asymmetric line-shape. Sharp plasmonic Fano resonances in nanohole sensors result in dramatic light intensity changes in response to the slightest excitation in the local environment. This light intensity change can be seen on the biosensor device with the naked eye without use of special optical detection instruments such as cameras and spectrometers.
Specifically, an extremely uniform nanostructure sensor chip containing certain ligands transmits particular wavelengths of light much more strongly than that predicted by classical aperture theory. When a test sample contains a particular analyte that is sought to be detected, the analyte binds to the ligand immobilized on the nanohole sensor chip. The ligand-analyte binding causes a shift in the wavelength of this extraordinary optical transmission (EOT), and the light intensity changes, which can be observed with the naked eye. Biosensor devices exploiting these Fano resonances have been used to directly detect a single monolayer of antibodies with the naked eye, and have far-reaching ramifications in personalized medicine and life science research. Id.
The illustration in FIG. 1 of the above-mentioned Yanik reference outlines how extremely uniform nanohole sensor can be fabricated using lift-off free evaporation (LIFE) nanolithography. FIG. 5 of the same reference illustrates that the extremely uniform nanohole sensor chip transmits EOT strongly, and that the EOT exhibit a shift in peak wavelength by about 22 nm when an analyte (e.g. mouse IgG antibody) in the test sample binds to capture molecules (e.g. protein A/G) immobilized on the nanohole sensor chip. The transmitted EOT light is filtered by a notch filter (WHM≈10 nm) spectrally tuned to the plasmonic resonances peak. As a result, the shift in peak wavelength causes a dramatic change in light intensity after the notch filter. Thus, an unfunctionalized control sensor exhibits a particular light intensity when viewed with a simple light source. A sample which does not contain the particular analyte that is sought to be detected exhibits a similar light intensity as the control because of non-specific binding. A sample that contains the analyte which is sought to be detected exhibits a different light intensity than the control because of the analyte-antibody specific binding. The differences in the light intensity can be distinguished with the naked eye.